package fly.leetcode.cn.q96;

class Solution {
    public int numTrees(int n) {
        int[] dp = new int[n+1];
        dp[0] = 1;
        dp[1] = 1;
        for (int i = 2; i <= n; i++) {
            for (int j = 0; j < i/2; j++) {
                dp[i] += (dp[j] * dp[i-j-1])*2;
            }
            if ((i&1) == 1){
                dp[i] += dp[i>>1] * dp[i>>1];
            }
        }
        return dp[n];
    }
}
